The present invention relates to a seal for ball screw, in particular, a seal useful for measures to dusts, dirt and the like against processed powder or spattering from such as laser beam machines. Further, the present invention also relates to a ball screw installing the seal.
As seals for ball screws for avoiding invasions of foreign matters such as dusts or machined powders from the exterior while driving the ball screw, a so-called wiper seal made of a felt, plastic or rubber has conventionally been used. A lip seal is excellent in a dust preventing performance and is less to create friction torque in a sealing part, and it has recently also been adapted to ball screws.
The lip seal is a doughnut-shaped disk of around 1 mm thickness composed of a material such as, for example, polyester elastomer or polyvinyl chloride, and the hole thereof is defined in such a manner that it mates with the cross sectional shape of the ball screw shaft and fits to the same with a slight interference. It is known that such a lip seal has the dust preventing performance far excellent than that of a brush wiper seal, and a generated friction toque is equivalent to or less than that of the brush wiper seal.
However, since the conventional lip seal for ball screws is, as seen in FIG. 7, formed to be particularly thin in the lip portion L at the front end of the inner circumference in the seal, rigidity is weak in a lateral direction (i.e., thickness direction) of the lip portion L. There is a problem wherein the front end of the lip portion L turns over while driving the ball screw. As seen in FIG. 7, as approaching up the upper part of the frank, in particular at the side contacting a frank opposite to the nut feeding direction in the screw shaft, and a space S probably appears, and consequently the dust preventing performance of the seal goes down.
Therefore, this invention has been realized in view of problems involved about the existing seal of ball screws. Accordingly, it is an object of the invention to provide a seal for ball screw that can effectively prevent invasions of foreign matters into the nut of the ball screw. The seal for ball screw according to the present invention is structured by improving the front end portion of the seal to be less to turn over the lip and cause a space thereby. In addition, it is an object of the present invention to provide a ball screw having such a seal for ball screws.
For accomplishing the above mentioned object, a first aspect of the invention is that a seal for a ball screw which has a sealing lip at an inside circumference of a sealing main body and is to be attached to a nut end portion of a ball screw, said sealing lip being adapted to the cross sectional shape of a ball screw shaft, characterized by providing projections at the front end portion of the sealing lip and at the side thereof being remote from the nut.
The projection has preferably a surface of circular-arc in cross section.
More preferably, the front end portion of the sealing lip also has a surface of circular-arc in cross section.
A second aspect of the invention is to structure the ball screw by attaching the seal for the ball screw as set forth in the first aspect to the nut end portion.
According to the invention, since the ring shaped projections are formed on the outer face in thin thickness of the front lip portion of the seal for ball screw, the rigidity is made strong along thickness. Accordingly, the front lip portion is difficult to turn over, which contacts the frank of the screw shaft opposite to the nut feeding direction during driving the ball screw to subsequently improve the dust preventing performance of the seal.
In addition, the above-mentioned object can be achieved by a seal for ball screw, according to the present invention, that comprises:
a sealing main body attached to a nut end portion of the ball screw; and
a sealing lip inwardly protruding from the sealing main body and extending substantially along a cross sectional shape of a ball screw shaft of the ball screw,
wherein the sealing lip includes:
a annular-shaped projection disposed at an end portion of the sealing lip.
Further, the above-mentioned object can also be attained by a ball screw, according to the present invention, comprising:
a ball screw shaft;
a ball screw nut movable along the ball screw shaft; and
a seal attached to an end portion of the ball screw nut, wherein the seal comprises
a sealing main body attached to a nut end portion of the ball screw, and
a sealing lip inwardly protruding from the sealing main body and extending substantially along a cross sectional shape of a ball screw shaft of the ball screw,
wherein the sealing lip includes
a annular-shaped projection disposed at an end portion of the sealing lip.
According to the invention, since the annular-shaped projection is formed on the end portion of the sealing lip, the rigidity is made strong along thickness. Accordingly, the front end portion of the sealing lip becomes difficult to turn over, to thereby improve the dust preventing performance of the seal.
In addition, in the above-mentioned construction according to the present invention, it is advantageous that the annular-shaped projection is disposed at one of side faces of the end portion of the sealing lip. With this advantageous construction, it is possible to improve a sealing ability, because of a double sealing operation that can be created by contacting both of the front end portion and the annular-shaped projection with the steeply oblique part of the frank surface of the screw shaft.